The present invention relates to a method and apparatus for securing machines, such as bending presses, against unwanted entries for preventing possible injuries.
The present invention is not limited for use in connection with bending presses and can equally be used on edging presses, punching machines, cutting machines and similar devices which have parts and components that execute potentially dangerous movements during a work cycle of the machine. Bending presses shape workpieces primarily by pressing them with a bending die against an opposing die or mold. The desired shape of the workpiece is attained by appropriately shaping the bending die and the associated mold. Frequently the bending die is a tool which is mounted on a first, movable machine part, while the mold is mounted in a second, fixed machine part. However, only the relative motions between the machine parts are important and, as an alternative, the mold can be movable or the die and mold can both move towards and away from each other. The safety system of the present invention can be used on all such machines.
It is well known that bending presses constitute a significant danger for operating personnel, especially danger of injury from tissue damage all the way up to the severance of body parts. It has been known for a long time that bending presses and the like must be protected with safety devices to prevent accidents. For example, German published patent application DE 010 38 223 A1 discloses a light grid safety system for a press. The light grid is formed by several individual light beams that are programmed and coupled to the movable tool part so that during a dangerous movement of a workpiece, only those light beams are activated which secure the zone beneath the moving tool part. The active zone of the light grid moves with the movement of the tool. When one of the light beams is interrupted, movement of the first tool part is stopped.
U.S. Pat. No. 5,579,884 discloses a light grid arrangement in which there are two or three light beams that are parallel to and run ahead of the leading edge of the bending die. When one of the light beams is interrupted, movement of the bending die is stopped. When only two light beams are used, they are arranged symmetrically on the frontal side of the machine, that is, on the side of the machine where the operator is located, and towards the aft, that is, the side of the machine remote from the operator. The same is true when three light beams are used, in which event the third light beam is accurately located beneath the leading edge of the bending die and has a greater spacing from the bending die than the two other light beams. In the arrangement of U.S. Pat. No. 5,579,884, the third light beam is primarily a control beam which prevents that a so-called muting point is set too low. The muting point (which means a point where the safety system is temporarily deactivated) occurs when, during a working cycle of the machine, the light beams of the safety device are temporarily deactivated. Without such temporary deactivation, the working cycle would not be completed when the workpiece being worked causes an interruption of a light beam.